A doubly-fed induction machine and the control in a single-phase grid connection

This paper proposes a drive system different from the conventional one using an inverter and rectifier or a back-to-back converter. It consists of a machine and an inverter without any input filter. Even though it has the simple structure, it can control the torque, speed and power quality of the connected grid simultaneously in variable speed. In the proposed system, the stator of the machine is directly connected to a single phase grid and the rotor is to a three phase inverter isolated from any power sources. The inverter can be integrated on the rotor or connected to it through the slip rings. The integrated configuration has merits in footprints and maintenances. In this paper, the possible operation areas in this topology are analyzed. The power balance of the rotor isolated from the grid is considered for the operation. The inverter of the rotor side can control the torque based on the vector control method while the rotor power is regulated. The power factor for the grid and shape of the grid current can be also controlled. The experimental results present the feasibility of the proposed system.